Robust capture of unknown objects with a highly under-actuated gripper.

Capturing large objects of unknown shape and orientation remains a challenge for most robotic grippers. We present a highly under-actuated gripper well suited for this task. Prior work shows two primary limitations to these grippers: the grip force of each link tends to decrease as the number of links increases, and the stability of an under-actuated linkage depends on the configuration of the links so grippers with many links are unlikely to be stable for arbitrary surfaces. We address these concerns by implementing two complementary methods of stabilization: using high-friction materials and scaling forces into the surface. We show that gecko-inspired adhesives provide an adhesion-controlled friction that can stabilize the gripper and improve grasp performance without the need of large normal forces. The under-actuated linkages also conform around arbitrary shapes and provide capability beyond prior adhesion-based grippers. With these high-friction interfaces, we show highly under-actuated linkages successfully grasp in many configurations without strict stability. The gripper is capable of holding over 30 N and consists of two tendon driven linkages that are each 65 cm long. This type of gripper is well suited for tasks without a predefined target geometry or orientation such as satellite servicing.